This invention relates to an apparatus for spreading particulate materials which is particularly but not exclusively designed for use in spreading granular fertilizer across the ground for agricultural use.
The application of granular fertilizer to the ground in a broadcasting action is well known and is employed very widely in agricultural practices. In more recent years chemicals have been added to the granular fertilizer generally as a liquid which is mixed with the granular fertilizer. The products thus applied to the ground have significantly enhanced effectiveness and accordingly it has become much more important to ensure accuracy of distribution. Thus a single pass of the machine should have accurately controlled metering so that a required amount of the material can be spread. In addition the material so metered should be accurately spread across the full width of the band covered by the machine. Furthermore the machine should have minimum delay or dwell between the actuation of a change in rate of the metered material, including stopping or start up, and the actual implementation of that rate change in the material as it is broadcast across the ground. With the machine running at 15 mph or higher, even a few seconds delay during which the material moves from the measuring point to the actual distribution point can result in a length of up to 150 feet of inaccurate rate of distribution.
Many devices available in the marketplace at the present time comprise simply a tank within which is mounted a conveyor belt which transports the material out through one end of the tank. A metering gate is provided at the point of exit from the tank so that a certain thickness of the material is carried out on top of the belt. The material is then simply deposited onto a spinner which rotates at high velocity throwing the material out vigorously in different directions. This technique is of course highly inaccurate in that different amounts of material will be spread at different positions across the ground and this technique is therefore basically unacceptable when used with the high technology products available at the present time. It does however retain a significant portion of the market based upon the low price.
The metering system of a device of this type is however well accepted in the trade and the use of a belt which is formed of stainless steel in hinged sections defining pockets in the belt for transporting the material forwardly is well known and well accepted. Belts of this type are of course entirely conventional and widely used.
The advantage of the spinner type device is of course that it is very inexpensive in comparison with more complex pneumatic distribution systems which are also available. One such pneumatic distribution system is shown in U.S. Pat. No. 4,475,819 (Balmer). This device which has led to a highly successful machine sold widely in U.S.A. and Canada includes a hopper within which the material is stored, a conveyor belt of a type described above which moves the material horizontally out of the hopper past a metering gate and discharges it into the lower end of a vertical auger. The auger transports material vertically and then spreads it readily into a number of ducts. An airflow generating in each of the ducts for transporting the material from the spreader assembly to discharge pipes of staggered length which extend outwardly from the spreader along a pair of booms to spread the material in a spread pattern across the ground. This device has been extremely successful but has two disadvantages. Firstly, the distribution system is relatively complex and hence expensive to manufacturer. Secondly, the vertical auger provides a significant dwell time of the material downstream of the metering point as explained above.
A further machine manufactured by New Leader of Cedar Rapids, Iowa is based upon a conventional machine using a spinner but in this case the spinner is replaced by a pair of booms each of which includes approximately nine pipes lying side by side in a horizontal plane and extending outwardly to the sides of the vehicle. The material from the metering belt falls from a discharge end of the belt into a number of cups. From the cups the material falls by gravity through flexible tubes which connect from the cup to the inner end of the pipes of the boom. From studying the brochures it appears that there must be some splitting arrangement since there are only nine cups apparently supplying the total of 18 pipes of the two booms. Air is supplied to the pipes from manifolds which connect to the end of the pipe by similar flexible tubes with the tubes being interleaved with the product supply tubes. This requires therefore tubes of reduced diameter relative to that of the pipes which of course can interfere with the required amount of flow of material and air and provides a horribly complex arrangement of plumbing. Furthermore, the boom height which is necessitated by the construction provided is very low on the order of fifteen inches from the ground which is unacceptable in field use due to the high probability of impact with the ground and due to the poor spread patterns obtained when the spreader nozzle at the outer end of the pipe is too close to the ground.
A further device manufactured by Tyler of Benson, Minn., includes a tank at the forward end of which is mounted a pair of booms with the pipes of each of the booms mounted in a single vertical plane. Above the booms is mounted a distribution box which is fed by an auger from the bottom of the tank so that material is lifted from the tank into the distribution box. Within the box is mounted a pair of belts of the type previously described which move in opposite directions outwardly from the center to the sides of the tank. At the outer sides of each of the belts, the material is discharged from the discharge end of the belt into a plurality of separate cups each of which connects through a flexible hose to a respective one of the pipes of the booms. In addition one of the cups from each side is connected through a long flexible pipe to a spreader at the rear of the vehicle.
This arrangement has achieved some success but retains a significant disadvantage of the complication necessitated by the provision of the auger lifting the material to the distribution box at the top of the tank so that it can fall by gravity into the pipes of the booms. Again, the flexible hoses provide a resistance to flow which significantly reduces the efficiency of the pneumatic transportation. However the metering of the material occurs on the belts just prior to the separation cups and hence the problem of the dwell has been significantly reduced.
A further alternative arrangement is manufactured by Valmar Airflow Inc. of Elie, Manitoba, Canada based upon a design developed by the present inventor. In this arrangement the metering is carried out by metering rollers which are arranged at the front of the tank and which discharge the material from the front of the tank into a plurality of cups. Each cup is connected with a venturi supplied with air from a manifold so that the material fed into the cup is injected into a flexible hose which extends from the front of the tank to the rear of the tank for communication with a respective one of the separate pipes of a pair of booms mounted at the rear of the tank. The booms are mounted with the pipes in vertical planes with the lifting of the material from the bottom of the tank to the height of the pipes of the booms being effected by the pneumatic transport which is relatively inefficient. This device is thus relatively complex and has low pneumatic efficiency and accordingly the disadvantages have limited the number of sales.
A further prototype device which has been sold in U.S.A. in very limited numbers and manufactured by Valmar under a further design of the present inventor is based upon the above-mentioned machine. However in this case both the metering and the booms are mounted at the rear of the tank. In addition the booms are mounted in a horizontal plane at the height of the bottom of the tank. A separate metering section is mounted at the rear of the tank and is fed by an auger system at the bottom of the tank which transports the material from the tank into the separate metering section under the control of a level detection switch within the metering section. The metering is carried out by a pair of rollers with the axes of the rollers parallel to the direction of movement of the vehicle, that is at right angles to the booms. The metering rollers thus meter the material out of the separate metering section directly into feed cups mounted on the pipes of the boom.
This device has been found to be impractical from a commercial point of view in view of the high complexity of the separate metering system and the low performance of the metering rollers which cannot provide the high variation in rate which is necessary for granular distribution systems of this type. This design has therefore been abandoned.
Other metering roller systems of a similar design to that of the above prototype are currently available from European manufacturers in which the material is metered by rollers with each roller being associated with a respective one of the booms. The rollers thus meter directly downwardly into the pipes of the booms which lie in a horizontal plane. As stated above this arrangement is unsatisfactory in that the metering rollers cannot provide the high variation in rates necessary, in that the metering rollers system has difficulty in accommodating the injection or application of liquid chemicals onto the granular fertilizer material and in that the system is relatively complex and therefore expensive.
Example of this prior European type system are Shown in U.S. Pat. No. 3,568,937 (Grataloup) and British Patent 1435176 (Amazonen).
A technique by which each duct or pipe of a boom is split to provide material to two separate spreader nozzles is shown in prior U.S. Pat. No. 4826088 of the present inventor.
Recapping, therefore, the currently available pneumatic devices for spreading of particulate material are generally unsatisfactory due to the high complexity and necessarily therefore a relatively high cost, due to the inadequacies of the roller metering system and due to the use with the belt metering system of flexible tubing which interferes with the efficiency of the pneumatic transportation and can introduce inaccuracies into the spread patterns generated by the machine.